I am sorry you are having trouble. I would encourage you to consider giving it another try, but if that is not in the cards, best of luck with whatever other software you decide to use.
I would like to say that what you posited above is not the way Inkscape works. "Last used style" is held over from the previous documents unless you change that preference, (and now that you have changed that preference there should be no problem) and the very first time you opened Inkscape it used the default (1px black, miter corners, IIRC) and made that the "last used style" until you changed it to whatever you needed for that document. Indeed, if you gave an object transparent or no fill and stroke, it would not be visible, and that would be the "last used style", but it is easy to change that by restyling.
Anyway, if you decide to persist, this list is generally quite helpful.

-Arlo James Barnes